Atmospheric Circulation Associated with Anomalous Variations in North Pacific Wintertime Blocking

Abstract

Atmospheric circulation associated with anomalous variation of North Pacific blocking during the northern winter (December to February) is described and examined using the National Centers for Environmental Prediction National Center for Atmospheric Research (NCEP-NCAR) reanalysis data from 1948/49 to 1999/2000. The divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells. There are several atmospheric cells over the North Pacific associated with an anomalous blocking situation during winter. They are the zonal Walker cell along the equator (ZWC), the regional Hadley cell in the western Pacific (WHC), the regional Hadley cell in the eastern Pacific (EHC), the regional Ferrel cell over the eastern Pacific in the midlatitudes (EFC), and the midlatitude zonal cell (MZC) over the Pacific. During a strong blocking winter (SBW), the ZWC is strengthened and the anomalous EHC is opposite to the anomalous WHC and the thermally driven Hadley cell. The anomalous MZC is characterized by air rising in the west part of the North Pacific, flowing eastward in the upper troposphere, descending in the eastern North Pacific, then returning back to the east coast of Asia in the lower troposphere, modulating the mean MZC. It is also found that the anomalous regional Ferrel cell at midlatitudes exists in the eastern Pacific (EFC), whereas it is not apparent in the western Pacific. All anomalous atmospheric cells almost completely reverse during a weak blocking winter (WBW). Evolutions of each cell are also investigated. The atmospheric cells over the tropical and subtropical regions (ZWC, EHC, and WHC) always emerge ahead of the anomalous blocking winter, and then lower troposphere signals propagate upward after the anomalous blocking winter. This may suggest a mid-to-low-latitude interaction of the response of the midlatitude atmospheric blocking to tropical SST variations and a feedback via the atmospheric cells to the Tropics. In contrast, the midlatitude cells (MZC, EFC) evolve very locally, with a simultaneous response to the blocking event and no propagation of signal.

Statistical downscaling of rainfall changes in Hawai‘i based on the CMIP5 global model projections

“…In our downscaled projections, the subtropical zonal dipole pattern constitutes a robust feature in multimodel ensemble projections. Although the dynamical reasons behind these circulation shifts are currently not well understood, an interplay between the position and extension of the Asian jet and subtropical cyclone activity and blocking events might play an important role in the central and eastern Pacific [ Chu , ; Huang et al ., ; Otkin and Martin , ; Jayawardena et al ., ]. Zonally aligned dipole‐like circulation anomaly patterns can be found in various mode decompositions of the atmospheric circulation [ Wallace and Gutzler , ; Barnston and Livezey , ; Johnson and Feldstein , ].…”

A key process of the nonstationary relationship between ENSO and the Western Pacific teleconnection pattern

“…The eddy heat and vorticity fluxes also induce rising motion poleward of the storm track and sinking motion farther equatorward 37 . In view of the association of rising (sinking) motion with upper-level divergence (convergence) 37 , 38 , a tropical convergence center over Philippines (10°N, 120°E) is likely associated with the subsidence branch of the Walker cell 38 . The midlatitude convergence region just north of the subtropical jet axis is characterized by an elongated zonal band of positive RWS, which likely manifests not only the subsidence branch of the thermally-driven local Hadley cell from the tropics but also those of the eddy-driven midlatitude zonal and meridional (local Ferrel-like) cells 38 associated with the STA.…”

Changes of the Boreal Winter Hadley Circulation in the NCEP–NCAR and ECMWF Reanalyses: A Comparative Study

“…The Helmholtz theorem (e.g., Arken 1985) states that the horizontal wind vector V may be divided into a rotational component V and a divergent component V d . The rotational part does not contribute to atmospheric divergences associated with vertical motion despite the fact that it is usually larger than the divergent part (Huang et al 2004). The zonal average of meridional divergent wind V d is the same as that of the total meridional wind.…”